1. Field of the Invention:
The invention relates to a process for the hydrogenation of liquid charge materials which contain carbon, such as heavy oils, oil residues, top or vacuum residues, syncrudes from oil shale, tar sands, tars and pitches from hard coal or brown coal, with gases which contain hydrogen as the hydrogenation gas, under the conditions of liquid phase hydrogenation at elevated temperature and elevated pressure, if necessary in the presence of an additive or even a catalyst, with a subsequent hot separator stage, with separate heating of a charge stream composed of the charge materials and a partial stream of the hydrogenation gas, and of a second partial stream of the hydrogenation gas. The charge materials are liquid either at normal temperature or at elevated temperatures.
2. Discussion of the Background:
The present invention relates to a process in which heavy oil is passed to a pre-heater as the charge product, and a partial stream of the entire hydrogenation gas amount required, which partial stream has been heated in a heat exchanger through which the hot separator head product flows, is added to the preheated mixture of heavy oil, additive, if necessary, and hydrogenation gas, before entry into the liquid phase reactor (cf. DE 35 23 709 Al).
In the known processes of this type, heating of the charge products to the temperature required for entry into the reaction system takes place by means of a heating furnace provided in the charge product stream. This heating furnace is one of the most critical components of any liquid phase hydrogenation system. This is particularly due to the operating conditions, characterized by high hydrogen partial pressure in the pipe, high pipe wall temperatures and high overall pressure, which set limits of operating technology for the material which can be used.
According to "Die Katalytische Druckhydrierung von Kohlen, Teeren und Mineralolen", Springer-Verlag, Berlin/Gottingen/Heidelberg 1950, page 232, heating of the reaction components basically takes place in heat exchangers and in the peak pre-heater. As heat exchangers, "bundle" regenerators are generally used, and for peak pre-heating by means of the externally heated heating furnace, hairpin-shaped pressure pipes with a clear diameter of 90 and 110 mm and a total length of about 30,000 mm are used, with the charge product stream being passed through the pipes and heated by means of circulating gas.
The process conditions, characterized by a multiphase stream of gases and vapors, liquid as well as solid in the pipe, result in significant uncertainties in designing of the heating furnace as well as in calculating the pressure loss and the heat transport.
The use of such peak pre-heaters is subject to disadvantages of process technology which result due to high pressure losses in the pre-heater, poor heat transfer as well as undefined conditions caused by the three-phase system present in the pipe.
Disadvantages in terms of operating technology result from the tendency towards encrustation of the interior of the furnace pipes and coking reactions of the product in the pipes. Further, operating time limitations of the hydrogenation system in total, as well as safety problems such as the occurrence of socalled "hot spots", can result in pipe ruptures.
Although it is indicated in DE 26 51 253 Al that the pre-heater heated with outside heat can be significantly reduced in size or possibly even eliminated entirely, what is provided instead is that a distillate fraction to be passed back into the charge product is heated again in a heat exchanger heated by outside heat. The additional heating of the distillates reportedly results in a significantly reduced tendency towards coking, as compared with heating of the coal slurry.